The present invention relates to magnet powder that is used as high performance permanent magnet and to a manufacturing method thereof, and to bond magnet therewith.
So far, as one kind of high performance permanent magnet, rare earth based magnets such as Smxe2x80x94Co based magnet, Ndxe2x80x94Fexe2x80x94B based magnet and so on are known. These magnets include much Fe or Co to contribute in an increase of saturation magnetic flux density. The rare earth elements such as Nd and Sm, due to behavior of 4f electrons in a crystal field, give rise to very large magnetic anisotropy. Thereby, coercive force is increased.
Such high performance magnets are mainly used in electrical appliances such as speakers, motors, measuring instruments and so on. In recent years, demand for downsizing various kinds of electrical appliances has increased. In order to cope with this, permanent magnet of higher performance is in demand. To such demands, compounds having TbCu7 crystal structure excellent in magnet properties and compounds containing nitrogen therein are proposed (cf. Japanese Patent Laid-open Application Nos. HEI 6-172936 official gazette and HEI 9-74006 official gazette, U.S. Pat. Nos. 5,480,495, 5,482,573, 5,549,766, 5,658,396, 5,716,462 or the like).
Magnet material having TbCu7 crystal structure as a principal phase is usually manufactured through a step of preparing master alloy, a step of heat treatment, and further a step of nitriding treatment. The step of preparing master alloy is implemented by use of liquid quenching method or mechanical alloying method. The step of heat treatment is implemented with the primary intention of controlling metallurgical structure of the master alloy. The step of nitriding treatment is applied with a primary intention of introducing nitrogen into interstitial positions of the principal phase to heighten crystal magnetic anisotropy of the principal phase.
In the step of nitriding treatment, it is usual to introduce nitrogen in the magnet material in the following way. That is, in an atmosphere containing nitrogen gas or nitrogen compound gas such as ammonia, the material is heat-treated to introduce nitrogen. At this point, so far, in order to increase an absorption efficiency of nitrogen, master alloy material such as quenched ribbon is milled so that an average particle diameter becomes approximately several tens Am to several hundreds xcexcm. After thereby increasing a specific surface area, heat treatment is implemented as a step of nitriding treatment.
In the step of nitriding treatment of the magnet material such as mentioned above, powder of smaller particle diameter absorbs nitrogen in excess during heat treatment to result in deterioration of magnetic properties. The existing nitrogen containing magnet material contains relatively much fine powder of which magnetic properties are deteriorated due to excess absorption of nitrogen. When much containing such fine powder, magnetic properties of magnet material as a whole deteriorates. From these reasons, in the magnet material thereto the nitriding treatment is implemented, it is demanded, by reducing an amount of fine powder that absorbs excess nitrogen, to suppress deterioration of magnetic properties.
Further, of the aforementioned manufacturing steps of the magnet material, in the step of quenching, ribbon-like alloy is prepared by use of for instance melt-spun method. In such allow ribbon (quenched ribbon), a fine crystalline phase (for instance, TbCu7 crystal phase) of an average crystal grain diameter of several nm to several tens nm is generated. Such fine crystal phase is an indispensable condition for obtaining high residual magnetization of the magnet material, resultantly for obtaining high maximum magnet energy product.
However, in the process of quenching due to the existing melt-spun method or the like, particle diameter of the principal phase consisting of TbCU7 crystal phase or the like is liable to scatter. As a result, deterioration of residual magnetization or the maximum magnetic energy product of the magnet material is liable to be caused. Thus, in view of an improvement of properties of the magnet material having TbCU7 crystal phase as a principal phase, it is important to control the particle diameter of the quenched ribbon that becomes forming material of the magnet material, the magnet material resultant therefrom. Accordingly, magnet material of which particle diameter is made fine with reproducibility and uniformity is demanded.
An object of the present invention is to provide magnet powder that enables, by reducing an amount of fine powder of which magnetic powder properties deteriorate during the nitriding treatment, to obtain excellent magnet properties with reproducibility and a manufacturing method thereof. another object of the present invention is to provide magnet powder that enables, by making crystal grain diameters of quenched ribbon uniformly fine, to obtain excellent magnetic properties with reproducibility and a manufacturing method thereof. Still another object of the present invention is provided bond magnet of high performance by using such magnet powder.
In order to overcome the aforementioned problems, present inventors carried out intensive studies. As the result, the following is found. That is, quenched alloy (for instance, quenched ribbon) prepared due to liquid quenching method, when used as a master alloy and provided to the step of nitriding treatment without milling into an average particle diameter of approximately several tens xcexcm to several hundreds xcexcm like in the existing method, magnet powder of high magnetic properties can be obtained.
That is, when a surface area of quenched alloy such as quenched alloy ribbon is put S, quenched alloy of which average value of surface area S is 0.5 mm2 or more or in which particles having a surface area S of 0.1 mm2 or more are 50% or more is used. To the aforementioned quenched alloy, heat treatment is applied to introduce nitrogen. Thereby, an amount of fine particles deteriorated in magnetic properties due to excess absorption of nitrogen or an influence of oxidation can be reduced. According to the magnet powder reduced in an amount of the fine particles like this, the magnetic properties of magnet powder as a whole can be heightened.
At this time, the quenched alloy such as quenched ribbon cracks due to an inclusion of nitrogen. Accordingly, even if an average value of the surface area S of the initial quenched alloy is as large as 0.5 mm2 or more, or even if particles of which surface area S is 0.1 mm2 or more are 50% or more, absorption efficiency of nitrogen does not deteriorate. Accordingly, the magnet powder therein a desired amount of nitrogen is introduced can be obtained.
A first invention is accomplished based on such findings. A first magnet powder of the present invention is characterized in having a composition expressed by the following formula;
general formula:
(R1XR2YBZT100xe2x88x92Xxe2x88x92Yxe2x88x92Z)100xe2x88x92QNQ
(in the formula, R1 is at least one kind of element selected from rare earth elements, R2 is at least one kind of element selected from Zr, Hf and Sc, T is at least one kind of element selected from Fe and Co, and X, Y, Z and Q are numbers satisfying respectively 2 atomic %xe2x89xa6X, 0.01 atomic %xe2x89xa6Y, 4xe2x89xa6X+Yxe2x89xa620 atomic %, 0xe2x89xa6Zxe2x89xa610 atomic %, and 0.1xe2x89xa6Qxe2x89xa620 atomic %), and TbCU7 crystal phase as a principal phase, a ratio of fine particles of which maximum diameter is 22 xcexcm or less being 20% by weight or less.
Alternatively, the magnet powder having a composition expressed by the aforementioned general formula and TbCu7 crystal phase as a principal phase is characterized in that a ratio of nitrogen content in atomic % of fine particles of which maximum diameter is 22 xcexcm or less to an average nitrogen content in atomic % of the magnet powder is 1.3 or less.
A manufacturing method of the first magnet powder of the present invention is characterized in comprising a step of manufacturing alloy having a composition expressed by;
general formula:
R1XR2YBZT100xe2x88x92Xxe2x88x92Yxe2x88x92Z
(in the formula, R1 is at least one kind of element selected from rare earth elements, R2 is at least one kind of element selected from Zr, Hf and Sc, T is at least one kind of element selected from Fe and Co, and X, Y, and Z are numbers satisfying respectively, 2 atomic %xe2x89xa6X, 0.01 atomic %xe2x89xa6Y, 4xe2x89xa6X+Yxe2x89xa620 atomic %, and 0xe2x89xa6Zxe2x89xa610 atomic %), and TbCu7 crystal phase as a principal phase, by use of a quenching method, and a step of implementing heat treatment for introducing nitrogen to the quenched alloy of which average value of the surface area S is 0.5 mm2 or less when the surface area of the quenched alloy is expressed by S.
Further, the inventors found that there is a close correlation between surface roughness of the quenched ribbon (alloy ribbon) that is prepared by use of liquid quenching method or the like and magnetic properties of magnet powder obtained therefrom. In the quenched ribbon and magnet powder resultant therefrom, by reducing the surface roughness thereof, magnetic properties of the magnet powder can be improved with reproducibility.
Smoothness of the surface of the quenched ribbon is closely related to wettability between molten melt and a roll during quenching. In general, bad wettability of the molten metal results in bad smoothness of the quenched ribbon, good wettability enables to produce the quenched ribbon of smooth surface. In the quenched ribbon of which wettability with the roll is excellent and surface roughness is small, difference of cooling speeds of a surface is contact with the roll and a free solidification surface is small. As a result, even if for instance a thickness of a ribbon is thick, whole material can be uniformly and sufficient quenched. Accordingly, the quenched ribbon as a whole, crystal grain diameter can be made fine with reproducibility and uniformity.
Further, the quenched ribbon of which surface is smoothed is preferably used in the later nitriding treatment in view of uniformly nitriding whole material. From these reasons, according to the magnet powder obtained from the quenched ribbon of small surface roughness, high magnetic properties can be obtained with reproducibility.
A second invention is achieved based on such findings. A second magnet powder of the present invention is characterized in having a composition expressed by;
general formula:
(R1XR2YBZT100xe2x88x92Xxe2x88x92Yxe2x88x92Z)100xe2x88x92QNQ
(in formula, R1 is at least one kind of element selected from rare earth elements, R2 is at least one kind of element selected from Zr, Hf and Sc, T is at least on kind of element selected from Fe and Co, and X, Y, Z and Q are numbers satisfying respectively, 2 atomic %xe2x89xa6X, 0.01 atomic %xe2x89xa6Y, 4xe2x89xa6X+Yxe2x89xa620 atomic %, 0xe2x89xa6Zxe2x89xa610 atomic %, and 0.1xe2x89xa6Qxe2x89xa620 atomic %), and having TbCU7 crystal phase as a principal phase, surface roughness of particles constituting the magnet powder being 5 xcexcm or less in terms of maximum height RY provided in JIS B 0601.
A manufacturing method of the second magnet powder of the present invention is characterized in comprising a step of manufacturing, by use of the liquid quenching method, allowing have a composition expressed by;
general formula:
R1XR2YBZT100xe2x88x92Xxe2x88x92Yxe2x88x92Z
(in the formula, R1 is at least one kind of element selected from rare earth elements, R2 is at least one kind of element selected from Zr, Hf and Sc, T is at least one kind of element selected from Fe and Co, and X, Y and Z are numbers satisfying respectively, 2 atomic %xe2x89xa6X, 0.01 atomic %xe2x89xa6Y, 4xe2x89xa6X+Yxe2x89xa620 atomic %, and 0xe2x89xa6Zxe2x89xa610 atomic %), and having TbCu7 crystal phase as a principal phase, so that the surface roughness thereof becomes 5 xcexcm or less in terms of maximum height Ry provided in JIS B 601.
Bond magnet of the present invention comprises a mixture of the aforementioned magnet powder of the present invention and binder, the mixture having a molded body of magnet shape.